<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    

    <script>

        //   反斜杠叫做转义字符

        //   .
        //   [  ] 
        //   /
        //   ?
        //   + 
        //   *

        var reg = /\+/ ;   // 两个\\

        console.log(reg.test('1+2./[3'));

    </script>
</body>
</html>